An SM-3 missile is launched from the USS Hopper on July 30, 2009. (Photo: MDA and U.S. Navy)

(CNSNews.com) – Ahead of the signing of a landmark U.S.-Russia nuclear arms reduction pact in Prague Thursday, the long-running contention between the two nations over missile defense shows no sign of easing.

Secretary of State Hillary Clinton reiterated Tuesday that the U.S. was “committed to pursuing” missile defense. She spoke at the Pentagon shortly after her Russian counterpart, Sergei Lavrov, repeated Moscow’s stance that it may withdraw from the new strategic arms reduction treaty (START) if it felt U.S. missile defense plans were beginning to threaten Russia.

Russia has maintained throughout that the U.S. plans could jeopardize its nuclear deterrent. The U.S. says the proposed system – initiated under the Bush administration and amended by President Obama last September – aims to protect against a potential Iranian missile attack and poses no threat to Russia’s deterrent ability.

The amended missile defense approach envisages a phased deployment, over a 10-year period, of interceptor missiles, starting with ship-borne missiles in southern Europe, gradually expanding westward and northward with the eventual goal of protecting all of Europe.

Lavrov acknowledged that the proposal, in its early stages, “will not create risks for Russia’s strategic nuclear forces.” But he said that if the developing system “begins to significantly affect the efficiency of Russian strategic nuclear forces,” Russia would have the right to opt out of the new START treaty.

(Arms control treaties typically contain a provision allowing a party to withdraw – after six months’ notice – if it considers its “supreme interests” to be in jeopardy. The now-expired START I treaty contained such a provision, as did the Anti-Ballistic Missile treaty, from which President Bush withdrew after 9/11, in order to pursue missile defense options.)

The pact to be signed by Obama and Russian President Dmitry Medvedev on Thursday, cutting the size of strategic weapons arsenals on both sides, will have to be ratified by the U.S. Senate, which generally supports missile defense, and the Russian Duma, which largely opposes it.

As such, the two administrations are emphasizing diametrically opposing interpretations of references, in the treaty’s preamble, to a link between strategic offensive and defensive weapons.

Lavrov on Tuesday described the linkage as “legally binding,” reinforcing a point contained in a Russian presidential statement on the accord, released by the Kremlin on March 26.

“The provisions on the interrelation between strategic offensive and strategic defensive arms, as well as on the growing significance of such interrelation in the process of strategic arms reduction, will be set in a legally-binding format,” the Kremlin document said.

By contrast, a White House statement released the same day declared, “The Treaty does not contain any constraints on testing, development, or deployment of current or planned U.S. missile defense programs or current or planned United States long-range conventional strike capabilities.”

U.S. officials continue to maintain that the language will impose no limits or constraints on proposed missile defense, and U.S. experts say that treaty preambles do not have legal power.

‘Unacceptable risk’

In a Ballistic Missile Defense Review released in February, the Pentagon noted that, if the U.S., NATO countries, Russia and China are taken out of the equation, there are around 5,900 ballistic missiles in existence around the world.

Against that background, Missile Defense Advocacy Alliance chairman Riki Ellison said Tuesday that any limitation of U.S. protection against current and future missile threats would entail “unacceptable risk” to American lives and national security.

“Any linkage to or limits of missile defense in the [START] treaty are seen as being contrary to U.S. national security and its ability to protect the homeland, troops, force structures overseas and allies from ballistic missiles,” he said.“The American public views Iran, North Korea, emerging terrorist groups and countries that sponsor those groups as the main threat to our national security, not Russia,” Ellison said.

“The American public and war fighter would not dare give up or limit its current and future defensive capability against those existent and emerging threats for a strategic arms control agreement with the Russians.”

Clinton said Tuesday that discussions would continue with the Russians “to try to find common ground around missile defense, which we are committed to pursuing.”

She said the U.S. has “persistently sought to explain” to them the important role missile defense can play in preventing proliferation and nuclear terrorism.

In his remarks Tuesday on the administration’s Nuclear Posture Review, Obama also highlighted the key role of missile defense in confronting the threat of nuclear terror and proliferation.

He said the NPR “recognizes that our national security and that of our allies and partners can be increasingly defended by America’s unsurpassed conventional military capabilities and strong missile defenses.”